Air bag having panels with different permeabilities

ABSTRACT

A vehicle air bag including a first panel of calendered uncoated fabric with a permeability of less than approximately 2 CFM at a pressure drop of 0.5 inches of water and at least one second panel of calendered uncoated fabric of the same yarn and weave type as the first panel operatively associated with the first panel. The at least one second panel has a permeability of greater than approximately 2 CFM at a pressure drop of 0.5 inches of water. At least one of the panels is constructed of a fabric having been processed to a controlled higher permeability subsequent to calendering.

This is a division of application Ser. No. 08/259,869, filed Jun. 15,1994, pending.

BACKGROUND OF THE INVENTION

The present invention relates generally to air bags of the type utilizedin vehicle occupant restraint systems. More particularly, the presentinvention relates to a vehicle air bag constructed substantiallyentirely of an uncoated fabric, as well as methods of producing such anair bag.

Virtually all motor vehicles in service today are equipped withseatbelts to restrain vehicle occupants during a collision. Recently,however, many vehicles have also been equipped with air bag systems tosupplement the protection provided by seatbelts. These air bag systemsutilize at least one folded air bag in fluid communication with a sourceof inflation gas. A sensor is provided to detect a collision between thevehicle and another object. When such a collision is detected, thesensor actuates the source of inflation gas. As a result, the air bag israpidly expanded to absorb at least a portion of the impact force whichwould otherwise have been imparted to the vehicle occupant.

Typically, the air bag is designed to inflate in a period whichgenerally corresponds to the "crash pulse" of the vehicle in which it isinstalled. For example, a vehicle having relatively "stiff" frame mayhave a crash pulse of approximately 30 milliseconds. In other words, aperiod of 30 milliseconds will elapse between the time in which acollision occurs at the front end of the vehicle and the time in whichthe force of such a collision is transmitted back to the vehicleoccupant and the cushion is fully inflated.

In contrast, a vehicle having a relatively "soft" frame may have a crashpulse of approximately 50 milliseconds or more. Thus, an air baginstalled in an exemplary vehicle having a relatively "stiff" frame maybe required to inflate 20 milliseconds or more faster than an air baginstalled in an exemplary vehicle have a relatively "soft" frame. Toeffect this faster inflation, a larger and more powerful source ofinflation gas will typically be required.

Air bags have generally been divided into two types, i.e. driver sideand passenger side. Driver side air bags have often been fitted into thevehicle steering column. These air bags, which typically have a circularconfiguration when fully inflated, have tended to be smaller because ofthe relatively small space between the driver and the steering wheel.

Passenger side air bags, on the other hand, have generally been fittedinto the vehicle dash ahead of the front seat passenger. Due to therelatively large space between the front seat passenger and the dash,these air bags have tended to be larger than driver side air bags. Whenfully inflated, a passenger side air bag will generally have a box-likeconfiguration.

Due to various considerations, driver side air bags and passenger sideair bags have often been constructed of different materials.Specifically, driver side air bags have frequently been constructed of abase fabric of either nylon or polyester which has been coated withchloroprene (neoprene), silicone or other appropriate elastomeric resinto reduce permeability. Passenger side air bags have generally beenconstructed of uncoated fabric.

It is important to design an air bag such that a specific rate ofdeflation is achieved. In other words, the air bag should quicklydeflate in a controlled manner as it is impacted by the vehicleoccupant. Adequate support will thereby be provided to the vehicleoccupant without excessive rebounding.

To achieve the desired rate of the deflation, driver side air bags havegenerally been constructed having relatively large vent holes throughwhich the inflation gas is expelled. It should be appreciated that anair bag intended to be used in a vehicle having a stiff frame willgenerally be required to deflate faster than an air bag for use in asoft frame vehicle. Thus, the specific size of these vent holes willgenerally be related to the crash pulse of the vehicle.

Because the inflation gas is generally very hot, the vent holes havetypically been defined in the rear panel of the air bag opposite thefront panel which is impacted by the driver. While face burns arelargely avoided by placing the vent holes in this location, finger andhand burns have often occurred. Additionally, relatively large ventholes often allow sodium azide particulate in the inflation gas toescape into the vehicle's passenger compartment.

Due to these problems, the air bag industry has developed variousalternative designs which do not have large vent holes. One such designis referred to as a "hybrid" air bag. The hybrid air bag is a driverside air bag utilizing a coated front panel which is generallyimpermeable to air, while having a back panel constructed of an uncoatedfabric. This uncoated fabric, like the uncoated fabric utilized toproduce many passenger side air bags, provides a degree of airpermeability by venting air through the fabric's natural interstices.

Prior art uncoated fabrics utilized in vehicle air bags rely heavily onprocessing parameters to control air permeability. For example,different air permeability values have often been achieved by adjustingsuch factors as yarn preparation, weaving, scouring or heat setting. Aproblem with attempting to achieve a specific air permeability in thismanner is that such processing parameters are often difficult to controlon a consistent basis. As a result, relatively large variations in airpermeability are often seen between respective lots of uncoated fabricwhich have ostensibly been prepared to the same permeabilityspecification. In fact, variations of +/- three (3) cubic feet perminute (CFM) at 1/2 inch of water pressure are not uncommon. These widevariations in permeability may undesirably result in large variations inthe deflation rates of respective air bags produced for a particularvehicle model.

SUMMARY OF THE INVENTION

The present invention recognizes and addresses the foregoingdisadvantages, and others of prior art constructions and methods.

Accordingly, it is an object of the present invention to provide animproved air bag for use in a motor vehicle.

It is a more particular object of the present invention to provide animproved vehicle air bag which is constructed substantially entirely ofan uncoated fabric.

It is a further object of the present invention to provide an improvedvehicle air bag constructed substantially of an uncoated fabric whichhas multiple panels of various permeabilities.

It is also an object of the present invention to provide an improvedfabric material for use in an air bag.

It is an additional object of the present invention to provide improvedmethods of producing a vehicle air bag.

Some of these objects are achieved by a vehicle air bag for use with anon-board inflator mechanism. When constructed as a driver side air bag,it may include a front panel of substantially uncoated fabric having apermeability of less than approximately two (2) CFM. A back panel ofuncoated fabric is also provided having a permeability of greater thanapproximately two (2) CFM. In presently preferred embodiments, the backpanel will have a permeability falling within a range of approximatelyfour (4) CFM to six (6) CFM. (Unless otherwise indicated, permeabilityvalues given herein are expressed with reference to a pressure drop of1/2 inch of water.) With the exception of a hole defined therein forproviding fluid communication with the on-board inflator mechanism, theback panel is substantially continuous throughout its extent.

The air bag may also be constructed as a passenger side air bag furtherhaving a body panel and a pair of side panels. In this case, the bodypanel will preferably have a permeability of less than approximately two(2) CFM, whereas the side panels will preferably each have apermeability of greater than approximately five (5) CFM. Preferably, thepermeability of the side panels will fall within a range ofapproximately five (5) CFM to seven (7) CFM.

Controlled permeability in the various panels may be achieved accordingto the invention by a multiplicity of needle punctures having a largerdiameter at a first side of the fabric than at a second side of thefabric. In this case, the fabric of the front or body panels may bearranged such that the first side defines a portion of an exterior ofthe air bag. Conversely, the fabric of the back and side panels may bearranged such that the first side defines a portion of an interior ofthe air bag.

Some objects of the present invention are also achieved by a method ofproducing a vehicle air bag constructed substantially entirely of anuncoated fabric. Preferably, a first step in such a method is to providean uncoated fabric of appropriate synthetic yarn. A first portion of theuncoated fabric may then be selectively processed to achieve a firstpreselected permeability. Next, a second portion of the uncoated fabricmay also be selectively processed to achieve a second preselectedpermeability which is higher than the first preselected permeability.The vehicle air bag may then be constructed utilizing the first portionand second portion of the uncoated fabric for various panels thereof.

In a presently preferred methodology, the first and second portions ofthe uncoated fabric are selectively processed by being calendered underselected temperature and pressure conditions to achieve a low referencepermeability. The portions are then further processed to increase aporosity thereof such that a selected permeability is achieved on aconsistent basis. In the case of a front panel of a driver side air bagor a body panel of a passenger side air bag, this controlledpermeability would generally be less than two (2) CFM. For a back panelof a driver side air bag this controlled permeability would generally begreater than approximately two (2) CFM, whereas a controlledpermeability of greater than five (5) CFM would generally be selectedfor side panels of a passenger side air bag.

This further processing may be accomplished by moving the uncoatedfabric at a selected speed past a plurality of needles reciprocating ata selected rate into and out of engagement therewith. In this case, aplurality of barbless needles are preferably utilized if the preselectedpermeability is less than a threshold permeability. If the preselectedpermeability is greater than the threshold permeability, a plurality ofbarbed needles are preferably utilized for this purpose. The thresholdpermeability may generally fall within a range of 3.0 CFM to 4.0 CFM,with a value of approximately 3.5 CFM being typical.

Alternatively, the uncoated fabric may be moved past a plurality offluid jets, preferably water jets, which impact the uncoated fabricunder selected operating conditions. Pores created by the fluid jets maybe set in the uncoated fabric by heat. As a result, the fabric willmaintain the desired permeability level during use.

Other object, features and aspects of the present invention arediscussed in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, to one of ordinary skill in the art, is set forthmore particularly in the remainder of the specification, includingreference to the accompanying figures, in which:

FIG. 1 is a back elevation of a typical prior art driver side air bag;

FIG. 2 is a side elevation of a driver side air bag constructed inaccordance with the present invention;

FIG. 3 is a perspective view of a passenger side air bag constructed inaccordance with the present invention;

FIG. 4 diagrammatically illustrates calendering of an uncoated fabric toselectively reduce the permeability thereof;

FIG. 5 diagrammatically illustrates needling of a calendered uncoatedfabric to selectively increase the porosity thereof;

FIGS. 6A and 6B respectively illustrate a barbless needle and a barbedneedle such as may be used in the needling apparatus of FIG. 5;

FIG. 7 diagrammatically illustrates a cross section of a calendereduncoated fabric which has been needled to show the configuration of therespective punctures; and

FIG. 8 diagrammatically illustrates a water jet apparatus which mayalternatively be used to increase the porosity of the uncoated fabric.

Repeat use of reference characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Referring now to FIG. 1, a typical driver side air bag of the prior artis indicated generally at 10. Air bag 10 includes a front panel (notshown) which is attached to a back panel 12 via stitching or otherappropriate means of such attachment. Back panel 12 defines an inflatorhole 14 to provide fluid communication with a source of inflation gas.As discussed above, the front panel and back panel 12 are each typicallyconstructed of fabric which has been coated with an elastomeric resin tobe practically impermeable to the passage of air. Accordingly, ventholes, such as vent holes 16 and 18, are defined in back panel 12 toexpel the inflation gas so that air bag 10 will quickly deflate asdesired.

As described above, the use of vent holes has often produced a number ofundesirable consequences, such as finger or hand burns and excessive gasparticulate. Additionally, air bags constructed of coated material tendto be more bulky than air bags constructed of uncoated material. Coatedmaterial is also generally more expensive to produce than uncoatedmaterial. As used herein, it is to be understood that the term "coated"refers to the coating of a fabric with some type of elastomer or thelike to reduce its air permeability. Thus, the term "uncoated" is notintended to preclude coating of the fabric with some other type ofmaterial having a relatively small weight in comparison with the basefabric for purposes other than reducing air permeability.

FIG. 2 illustrates a driver side air bag 20 of the present inventionwhich is constructed substantially entirely of uncoated fabric. Air bag20 has a back panel 22 and a front panel 24 attached about theirrespective circumferences by stitching or other appropriate means ofsuch attachment. Back panel 22 defines therein an inflator hole 26, butpreferably is otherwise continuous throughout its extent. In otherwords, back panel 22 may be generally devoid of large vent holes, suchas vent holes 16 and 18 of air bag 10.

Instead of relying upon the natural interstices of the fabric to provideventing, the uncoated fabric of back panel 22 and front panel 24 hasbeen processed according to the invention to provide a controlledpermeability. As indicated by the relative occurrence of stippling inFIG. 2, back panel 22 will preferably have a greater permeability thanfront panel 24. In presently preferred embodiments, the permeability ofback panel 22 is greater than approximately two (2) CFM, often fallingwithin a range of approximately four (4) CFM to six (6) CFM. In anexemplary construction, the permeability of back panel 22 may fallwithin a range of five (5) CFM to six (6) CFM. Front panel 24 willgenerally have a permeability of less than two (2) CFM.

FIG. 3 illustrates a passenger side air bag 28 of the present invention.Air bag 28 is also constructed substantially entirely of uncoatedfabric, which has not been uncommon in passenger side air bags of theprior art. Air bag 28 differs from the prior art, however, in thatrespective panels thereof are produced according to the invention tohave a controlled permeability. As a result, greater consistency indeflation may be achieved.

A body panel 30 forms a top, front and bottom portion of air bag 28.Preferably, body panel 30 has a permeability of less than two (2) CFM. Aleft side panel 32 and a similar right side panel (not shown) arestitched or otherwise attached to body panel 30. The controlledpermeability of such side panels is preferably greater than five (5)CFM, and may generally fall within a range of approximately five (5) CFMto seven (7) CFM. Air bag 28 further includes a snout assembly 34 toprovide fluid communication with the source of inflation gas.

Presently preferred methods by which controlled permeability may beachieved in the fabric utilized in air bags 20 and 28 may be bestunderstood with reference to FIGS. 4 through 8. According to at leastone exemplary technique, an important step in providing this controlledpermeability is to stabilize the permeability of the fabric at a lowreference permeability. Once this low reference permeability isachieved, further processing may be utilized to selectively increasefabric porosity. The amount and character of such further processingwill then determine the final permeability of the fabric.

The low reference permeability is preferably achieved by calendering, asillustrated in FIG. 4. In this regard, a supply roll 38 providesuncoated fabric 40 of the type which is appropriate for use in an airbag. A number of specifications for air bag fabric are well known,including weight, thickness and strength. Preferably, the fabric ofsupply roll 38 will be either woven or warp knitted fabric constructedsubstantially entirely of synthetic fibers. Because nylon is somewhathygroscopic, i.e. water absorbing, presently preferred embodiments mayfrequently utilize polyester yarn. Such yarn may have a size of 600denier or other yarn size appropriate for the exigencies of a particularapplication.

Fabric 40 is delivered from supply roll 38 into a calender device 42,which includes a relatively large center roller 44 and a pair of smallerrollers 46 and 48. As shown, fabric 40 extends between rollers 44 and 46and then around roller 48. After leaving calender device 42, fabric 40is delivered to take up roll 50 as illustrated.

Rollers 46 and 48 apply heat and pressure onto contiguous portions ofcenter roller 44. As a result, fabric 40 is calendered on one side attwo nip locations 52 and 54. It has been found that calendering fabric40 at a temperature of 300 degrees Fahrenheit and a pressure of 3000lbs. per square inch produces a reference permeability of less than one(1) CFM, as is generally desired according to presently preferredmethodology.

After the reference permeability is achieved, further processing isutilized to raise the overall permeability of the fabric to a desiredlevel. FIG. 5 illustrates one presently preferred method which may beutilized for this purpose. As shown, fabric 40 is moving in thedirection of arrow A under the influence of an appropriate conveyormechanism 56. A needle carrier 58 having thereon a plurality of needles(referenced generally as 60) is shown reciprocating into and out ofengagement with fabric 40, as indicated by arrow B. Preferably, needles60, which may generally have a size of 18 gauge to 40 gauge, will engagethe calendered side of fabric 40.

The density of needles 60 (in number of needles per unit area), alongwith the speed of fabric 40 and the rate of reciprocation of carrier 58(as measured in strokes per minute (SPM)) gives a characteristic numberof punctures per square inch (PPSI). It has been found that, for aparticular needle size operating under defined conditions, a PPSI valuemay be selected to achieve a desired permeability with greaterconsistency than has generally been achieved by relying only uponprocessing parameters as has been the case in the past. In fact, it hasbeen found that a particular air permeability may be achieved accordingto the invention with a variation of less than approximately +/- 1.0CFM, as opposed to the +/- 3.0 CFM as was common in the prior art.

When relatively low levels of permeability are desired, needles 60 arepreferably barbless needles, such as needle 60A of FIG. 6A. As shown,needle 60A includes a conical tip portion 62 integrally extending into atapered shaft portion 64. Because of the shape of tapered shaft portion64, greater permeability may often be produced at a given PPSI level byincreasing the depth of needle penetration.

With barbless needles, it has been found that upon achieving a certainthreshold permeability, further needling becomes largely ineffective toprovide additional increases in permeability. Generally, this thresholdpermeability will fall within a range of 3.0 CFM to 4.0 CFM, with avalue of approximately 3.5 CFM being typical.

If it is desired that the permeability of fabric 40 be greater than thisthreshold permeability, a barbed needle, such as needle 60B of FIG. 6B,may be utilized. Like needle 60A, needle 60B includes a generallyconical tip portion 66 integrally extending into a tapered shaft portion68. However, needle 60B further includes at least one barbed portion 70which functions to enlarge the size of the puncture created when fabric40 is engaged. It should be appreciated that, while a barbed needlecould be utilized to produce permeabilities below the thresholdpermeability, such is often not desired. This is because the use of abarbed needle creates a rougher fabric surface, which may not bedesirable in panels (such as front panel 24 of air bag 20 and body panel30 of air bag 28) which may come into contact with the face of a vehicleoccupant.

FIG. 7 diagrammatically illustrates a plurality of punctures 72 whichmay be produced in fabric 40 by needling as described. As shown, theconical configuration of needles 60 produces punctures 72 which have agreater diameter at a first side 74 of fabric 40 than at a second side76 of fabric 40. This generally produces a more laminar flow as gasmoves through punctures 72 from side 74 to side 76 than vice versa. As aresult, the permeability of fabric 40 is generally greater when side 74is situated on an interior of the air bag. Thus, to provide a lowerpermeability in front of the occupant's face, front panel 24 of air bag20 and body panel 30 of air bag 28 are configured having first side 74on the exterior. Further smoothness is provided to the occupant's faceby the fact that side 74 is also preferably the side which has beencalendered. Other areas of air bags 20 and 28 are preferably constructedhaving first side 74 on the interior to enhance permeability.

An alternative methodology of producing a controlled permeability infabric 40 is illustrated in FIG. 8. In this case, fabric 40 is shownmoving beneath a plurality of fluid jet headers 78 under the influenceof an appropriate conveyor mechanism 80. Each of headers 78 emits aplurality of fluid jets, which strike fabric 40 with predeterminedoperating characteristics. As a result, pores are created to allow thefluid to flow therethrough.

Several factors will affect the permeability of fabric 40 produced in afluid jet system, such as that illustrated. In addition to total fluidenergy delivered, such factors include the number of orifices in each ofheaders 78, as well as the spacing and size of these orifices.Generally, conveyor 80 will include a wire mesh substrate which fabric40 will have a tendency to mimic as it is impacted by the fluid jets.Thus, the type of substrate will also affect the permeability, as wellas whether the fluid jet system is flat as illustrated or a rotary typesystem. In order to permit lower jet energies to form these pores,fabric 40 is preferably uncalendered when this method is utilized.

Preferably, the fluid jets emitted by header 78 are water jets. Thiswater is shown being collected in respective collection basins 82 fromwhich it is carried away. It can be seen that the system of FIG. 8 issimilar to a "hydroentanglement" system of the type utilized to producenonwoven materials. Some of the principals of a hydroentanglementapparatus are described in U.S. Pat. No. 3,494,821, issued Feb. 10, 1972to Evans, which is incorporated herein by reference.

Generally, nonwoven material produced in a hydroentanglement apparatusis subjected to a relatively strong vacuum to remove absorbed water.However, when used with a woven fabric, such as fabric 40, a vacuumtreatment of this type will generally tend to make fabric 40 have arelatively stiff "hand." To retain a relatively "soft" hand, fabric 40is preferably dried in a tenter oven 84. Oven drying in this manner mayalso serve to heat set the pores formed by the fluid jets. As a result,such pores will remain in fabric 40 to give the desired air permeabilitylevel. In this regard it is desirable that, once dry, that fabric 40remain heated to a temperature of approximately 350 degrees Fahrenheitto 380 degrees Fahrenheit for a period exceeding approximately 20 to 30seconds.

It can thus be seen that the invention provides an improved technologyfor constructing an air bag substantially entirely of uncoated materialwhile achieving a more consistent permeability than was generallyachievable with the prior art. While presently preferred embodiments ofthe invention and presently preferred methods of practicing the samehave been shown and described, it should be understood that variousmodifications and variations may be made thereto by those of ordinaryskill in the art. In addition, it should be understood that aspects ofthe various embodiments may be interchanged both in whole or in part.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only and it is not intendedto be limitative of the spirit and scope of the invention so further setforth in the following claims.

What is claimed is:
 1. A vehicle air bag for use with an on-boardinflator mechanism, said vehicle air bag comprising:a first panel ofcalendered uncoated fabric having a permeability of less thanapproximately 2 CFM at a pressure drop of 0.5 inches of water; and atleast one second panel of calendered uncoated fabric of a same yarn andweave type as said first panel operatively associated with said firstpanel, said at least one second panel having a permeability of greaterthan approximately 2 CFM at a pressure drop of 0.5 inches of water, atleast one of said panels being constructed of a fabric having beenprocessed to a controlled higher permeability subsequent to calendering.2. A vehicle air bag as set forth in claim 1, wherein at least one ofsaid panels is characterized by a multiplicity of needle puncturestherein.
 3. A vehicle air bag as set forth in claim 2, whereinrespective of said multiplicity of needle punctures generally have alarger diameter at a first side of the calendered uncoated fabric thanat a second side of the calendered uncoated fabric.
 4. A vehicle air bagas set forth in claim 3, wherein both said first and second panelsinclude said needle punctures therein and wherein said calendereduncoated fabric of said first panel is arranged such that said firstside defines a portion of an exterior of said air bag and saidcalendered uncoated fabric of said at least one second panel is arrangedsuch that said first side defines a portion of an interior of said airbag.
 5. A vehicle air bag as set forth in claim 1, wherein said air bagis a driver's side air bag such that said first panel is a front paneland said second panel is a back panel thereof, said back panel beingsubstantially continuous excepting a hole defined therein for providingfluid communication with an on-board inflator mechanism.
 6. A vehicleair bag as set forth in claim 5, wherein said back panel has apermeability of at least approximately 4 CFM at a pressure drop of 0.5inches of water.
 7. A vehicle air bag as set forth in claim 5, whereinsaid back panel has a permeability falling within a range ofapproximately 4 CFM to 6 CFM at a pressure drop of 0.5 inches of water.8. A vehicle air bag as set forth in claim 1, wherein said air bag is apassenger side air bag having at least two of said second panels formingrespective of a pair of side panels thereof, said side panels eachhaving a permeability of at least approximately 5 CFM at a pressure dropof 0.5 inches of water.
 9. A vehicle air bag as set forth in claim 8,wherein said pair of side panels respectively have a permeabilityfalling within a range of approximately 5 CFM to 7 CFM at a pressuredrop of 0.5 inches of water pressure.
 10. A vehicle air bag for use withan on-board inflator mechanism, said vehicle air bag comprising:a firstpanel of calendered uncoated fabric having a permeability of less thanapproximately 2 CFM at a pressure drop of 0.5 inches of water; and atleast one second panel of calendered uncoated fabric operativelyassociated with said first panel, said at least one second panel havinga permeability of greater than approximately 2 CFM at a pressure drop of0.5 inches of water, wherein at least one of said first and secondpanels is characterized by a multiplicity of needle punctures therein.11. A vehicle air bag as set forth in claim 10, wherein respective ofsaid multiplicity of needle punctures generally have a larger diameterat a first side of the calendered uncoated fabric than at a second sideof the calendered uncoated fabric.
 12. A vehicle air bag as set forth inclaim 11, wherein both said first and second panels include said needlepunctures therein and wherein said calendered uncoated fabric of saidfirst panel is arranged such that said first side defines a portion ofan exterior of said air bag and said calendered uncoated fabric of saidsecond panel is arranged such that said first side defines a portion ofan interior of said air bag.